In order to improve the stability of high density polyethylene (HDPE) as a thermal energy storage medium, HDPE was cross-linked by electron beam irradiation. Solid state NMR spectroscopic methods were used to analyze the cross-linked HDPE and its thermal degradation. The influence of ethylene glycol (EG) as a heat transfer fluid on the cross-linked HDPE was also investigated. Neither oxidation nor phase transition was observed in HDPE kept in vacuum, even after 1000 h at 1508C. However, both phenomena were observed in HDPE either kept at 1508C or thermally cycled in air. HDPE completely immersed in EG was not oxidized, but phase transition from crystalline to amorphous, probably caused by the penetration of EG into the HDPE, was detected. The observed increase of amorphous phase was attributed to a result of crystalline to amorphous phase transition of perturbed regions in the crystalline phase close to defect sites occupied by oxidation products or EG molecules.
Посилання на статтю:
High density polyethylene as a thermal storage material studied by MAS 13 C NMR spectroscopy / O.H. Han, S.A. Chae, S.O. Han, S.K. Woo // Polymer. – 1999. – N 40. – P. 6329–6336.